1. Field of the Invention
This invention generally relates to transmission of Sync Channel Messages in digital wireless mobile communications systems. In particular, the present invention relates to operation of Sync Channel Messages transmitted by a base station according to an Interim Standard (IS-2000) Rev. A System, to multiple-configured mobile stations, including IS-95 Mobile Stations, and IS-2000 Rev. A Mobile and beyond
2. Background Art
The first global standards for Code Division Multiple Access (CDMA) systems are TIA/EIA IS95 standards that were published by Telecommunications Industry Association (TIA) in 1993. Since then, the standards have been improved and evolved, which can be distinguished by their protocol revision number (P_REV). For example, the P_REV of IS95-B standard with all required features is P_REV=5 and that of IS-2000 Revision 0 standards is P_REV=6. Also, the IS-2000 Revision A standards has a P_REV value of P_REV=7 and the most recent version of CDMA specification, that is IS-2000 Revision C, has P_REV=10.
FIG. 1 is a diagram illustrating mobile station (MS) states as a CDMA mobile station is powered on. The MS first enters a Mobile Station Initialization State (100) having four substates, namely a System Determination Substate 101, a Pilot Acquisition Substate 102, a Sync Channel Acquisition Substate 103, and Timing Change Substate 104. In the System Determination Substate 101, the MS selects the system to lock on and then the MS acquires pilot channel in step 102 and sync channel in step 103. After the MS correctly receives the Sync Channel Message (SCHM) in step 103, the MS synchronizes its long code timing and system timing to those of the CDMA system during the Timing Change Substate 104. The MS then enters the Mobile Station Idle State 110 in which the MS is monitoring the overhead message and paging message from the Base Station (BS).
The evolution of CDMA system has resulted in the redistribution of messages throughout different channels. For example, the overhead and paging messages in the IS95-B systems and IS-2000 Rev. 0 systems are sent on the Paging Channel (PCH), one of the physical channels sent from the BS. The IS-2000 Rev. A systems, however, added the Forward Common Control Channel (F-CCCH) and Broadcast Control Channel (BCCH) to enhance the performance; hence, in the IS-2000 Rev. A Systems, the paging messages are sent on the F-CCCH and overhead messages are sent on the BCCH.
The differences between the IS-95B, IS-2000 Rev. 0 and IS-2000 Rev. A systems are summarized in Table 1:
TABLE 1(Channel)IS-95BIS-2000 Rev. 0IS-2000 Rev. ASCHMP_REV = 5P_REV = 6P_REV = 7MessageMessage Length =Message Length >=Length <28 Octet28 Octet28 Octet11-bitAdded message(EXT_CDMA_FREQfields containfield newly added)BCCH info.PagingUsed to sendUsed to send[Used only to sendChannelpaging andpaging and overheadpaging and overheadoverheadmessagesmessages formessagesbackward compati-P_REV = 5bility of older MSs;in the ESPMpaging channelfunctions moved toBCCH/F-CCCH]BCCH/N/AN/ABCCH used to sendF-CCCHoverhead messageF-CCCH used tosend paging message
The paging channel is no longer used in IS-2000 Rev. A systems except when older-version of MSs (e.g. IS-95B or IS-2000 Rev. 0) are present in the Rev. A system.
To support the BCCH, the Sync Channel Message (SCHM) of IS-2000 Rev. A systems was extended by additional fields that contain the various information regarding the BCCH, such as Code Rate of BCCH, Data Rate of BCCH, Transmit Diversity of BCCH, etc.
The length of Sync Channel Message (SCHM) in IS95-B system is 27 Octets. But in IS-2000 Rev. 0 system, the 11-bit EXT_CDMA FREQ field was added to the SCHM and the length of SCHM was extended to 28 Octets, which caused some of IS-95 Legacy Mobile Stations (MS) from some particular manufacturers, especially from Nokia and Motorola, having difficulty to recognize the extended SCHM. The IS-95 MSs from Motorola and Nokia reliably obtain the SCHM only when the length of SCHM is same as that of IS-95B SCHM (27 octets).
A solution to the problem of reliably obtaining the SCHM, named the “IS-2000 Rev. 0 Workaround Solution”, was proposed and adopted as a method to solve this problem without changing any standards. The IS-2000 Revision 0 Base Station (BS) sets P_EV value in the SCHM to ‘5’ and later, the BS lets the MS know the “true P_REV” which is ‘6’ through the Extended System Parameters Message (ESPM) that is sent in the Paging Channel. The ESPM is one of the overhead messages that is sent through Paging Channel to give the MS parameters regarding the corresponding System. The EXT_CDMA_FREQ message can be specified in the CDMA_FREQ field that is sent in the Extended CDMA Channel List Message (ECCLM) which is also sent in the Paging Channel. The ECCLM is another one of the overhead messages sent through Paging Channel to give the MS information regarding the frequencies that the BS uses.
FIGS. 2A, 2B, and 2C are diagrams illustrating IS-2000 Mobile Station responses to different wireless systems. The IS-2000 Revision 0 Workaround Solution was made possible without changing any standards because there was a CDMA_FREQ field in the ECCLM. FIG. 2A illustrates the normal operation of an IS-2000 Rev. 0 MS within an IS-2000 Rev. 0 system: the MS receives in step 112 the SCHM having a P_REV=6; the MS changes in step 114 the frequency specified in the EXT_CDMA_FREQ field in the SCHM message, obtains the paging channel, and enters its idle state.
FIG. 2B illustrates an IS-2000 Rev. 0 MS within an IS-2000 Rev. 0 system, where the system uses the IS-2000 Rev. 0 Workaround Solution. The MS receives in step 116 a SCHM having a P_REV=5, with no EXT_CDMA_FREQ field included in the SCHM. The MS receives in step 118 the paging channel at the same frequency as the SCHM in step 118. The MS determines in step 119 that the true P_REV is P_REV=6 from the ESPM sent on the paging channel. The MS changes in step 120 the frequency specified by the CDMA_FREQ field in the ECCLM of the paging channel, and enters its idle state. The workaround solution causes some delay while the MS gets the paging channel, however, the MS can get the frequency information.
FIG. 2C illustrates normal operation of an IS-2000 Rev. A MS located within an IS-2000 Rev. A system. In this case, more parameter fields were added to the SCHM to support the Broadcast Control Channel (BCCH). The MS obtains in step 122 the SCHM specifying the P_REV=7, and changes in step 124 the frequency specified by the SCHM and obtains the BCCH. The MS then enters its idle state. Note that in the IS-2000 Rev. A system, no new messages are added to the paging channel that contain information on BCCH. The new parameters are sent only in the SCHM. Hence, if the IS-2000 Rev. A BS sends the SCHM with P_REV set to 5, the problem MS from Motorola and Nokia will work well but the IS-2000 Rev. A MS cannot get information related to BCCH from anywhere. If the IS-2000 Rev. A BS sends the SCHM with P_REV set to 7, the problem MSs will not work since they cannot get the SCHM with the length beyond 28 Octets.
The detailed symptoms of problem MSs are as follows:
Nokia IS95 MS: FIG. 3 illustrates the structure of the Sync Channel super frame. The Sync Channel super frame 132 has 3 Sync Channel frames 130. Nokia IS95 MSs were made to add two frames to the received SCHM to estimate the super frame boundary since the length of IS95 SCHM is composed of 7 Sync Channel frames. Hence, the Nokia MSs can align the super frame boundary correctly only when the length of SCHM is (3n+1) frames, where n is an integer greater than 0.
Motorola IS95 MSs are made to reject the SCHM of which the length is greater than 32 Octets. When the length of SCHM is greater than 28 octets, some of the Motorola IS95 MSs go through some delay before they gets the SCHM correctly, the reason of which is unknown. (28 Octet problem).
However, the proposed “IS-2000 Rev. 0 Workaround Solution” would require an additional change in the existing Wireless Specifications IS-2000 Rev. 0 and IS-2000 Rev. A Such a change in the existing Wireless Specifications would adversely affect deployment of newer wireless standards due to the risk of ad hoc changes to the specifications destabilizing design work according to specifications that were considered completed.